1. Field of the Invention
The present invention relates to an adaptive encoding system of a moving picture signal and, in particular, relates to a system which uses an orthogonal transform for each small blocks in a picture frame.
2. Description of the Related Art
In a prior art system which encodes a picture signal through orthogonal transform, a picture frame is divided into a plurality of small blocks, each of which is subject to orthogonal transform to provide transformed signal matrix. The coefficients in the matrix are quantized, and encoded into a variable length code. In this case, in order to reduce bit rate of encoded picture signal so that a quantized picture frame is transmitted through a transmission circuit of a predetermined fixed bit rate, a step size of a quantizer is selected through feedback system which has a buffer memory for storing matrixes. The step size is systematically determined so that the memory does not overflow. In other words, when the memory is not near capacity, a small step size is selected to provide a fine picture, and when the memory is near capacity, a large step size is selected to provide a coarse picture.
However, the prior art system has the disadvantage in fast processing that the selection of a step size is subject to time delay because of feedback loop in a memory circuit operation, and the memory is subject to overflow. When the memory overflows, the step size must be considerably large, so that picture quality is much deteriorated.
Another disadvantage of the prior art system is that the information reduction in encoding is insufficient.
Still another disadvantage of the prior art system is that the step size does not depend upon the picture pattern.